题解 | 24点游戏算法

#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;

double cal(double a, double b, char c) {
    switch (c) {
        case '+' :
            return a + b;
        case '-' :
            return a - b;
        case '*' :
            return a * b;
        case '/' :
            return a / b;
    }
    return 0;
}

bool check(vector<double> v) {
    char op[4] = {'+', '-', '*', '/'};
    sort(v.begin(), v.end());
    do {
        for (int i = 0; i < 4; i++) {
            for (int j = 0; j < 4; j++) {
                for (int k = 0; k < 4; k++) {
                    if (abs(cal(cal(cal(v[0], v[1], op[i]), v[2], op[j]), v[3],
                                op[k]) - 24) < 1e-6 ||
                            abs(cal(cal(v[0], cal(v[1], v[2], op[j]), op[i]), v[3], op[k]) - 24) < 1e-6 ||
                            abs(cal(cal(v[0], v[1], op[i]), cal(v[2], v[3], op[k]), op[j]) - 24) < 1e-6 ||
                            abs(cal(v[0], cal(cal(v[1], v[2], op[j]), v[3], op[k]), op[i]) - 24) < 1e-6 ||
                            abs(cal(v[0], cal(v[1], cal(v[2], v[3], op[k]), op[j]), op[i]) - 24) < 1e-6) {
                        // cout<<v[0]<<op[i]<<v[1]<<op[j]<<v[2]<<op[k]<<v[3];
                        return true;
                    }
                }
            }
        }
    } while (next_permutation(v.begin(), v.end()));
    return false;
}

int main() {
    vector<double> v(4);
    while (cin >> v[0] >> v[1] >> v[2] >> v[3]) { // 注意 while 处理多个 case
        if (check(v)) {
            cout << "true" << endl;
        } else {
            cout << "false" << endl;
        }
    }
}
// 64 位输出请用 printf("%lld")